The present invention relates to an anti-icing composition suitable for use on a variety of substrates, and which is particularly suited for use on substrates related to aircraft environments.
Various modes of transportation are at risk of dire consequences due to the build-up of ice during cold or winter conditions. Aircraft that are either parked on the ground or are on the ground between flights can accumulate snow, ice, freezing rain, or frost on the aircraft surfaces and aircraft engine components in cold weather. Such accumulation, particularly on airfoil surfaces, is generally an unsafe airfoil condition in that it hampers and can stop liftoff. Additionally, ice build up during flight can be a problem. The jet engines of airplanes are also at risk of unexpected flame out if ice builds up on certain components of the engine. Additionally, such ice buildup may break off into large chunks which when impacted against components of the engine can cause significant damage. Thus, there is a need for a coating that can effectively reduce the amount of ice build up on surfaces, including those on aircraft, under harsh weather conditions.
The anti-icing composition of the present invention includes a glassy matrix preferably formed by crosslinking a mixture of a functionally-terminated silicone and an alkoxy-functionalized siloxane to provide an interpenetrating polymer network (xe2x80x9cIPNxe2x80x9d) of glass and silicone. Grafted to the matrix is a material capable of microphase separation. The material capable of microphase separation is at least two liquid materials, at least one of which is graftable to the matrix. Also included in the material is a freezing point depression agent such as a polyol or salt hydrate. Such a freezing point depression agent may itself be a material capable of microphase separation.
In an alternative embodiment, the present invention provides an anti-icing composition comprising a crosslinked mixture of an epoxy, an alkoxy-functionalized siloxane and a compound (e.g., silane) capable of compatabilizing the epoxy and the alkoxy-functionalized siloxane to provide an epoxy-modified interpenetrating polymer network of glass and epoxy. Grafted to the matrix is the material capable of microphase separation. The composition also includes a freezing point depression agent.
The present invention also provides a substrate such as an airplane wing coated with either the composition including the interpenetrating polymer network of glass and silicone or the composition including the interpenetrating polymer network of glass and epoxy.
The present invention will be more fully understood by reference to the following description and examples. Variations and modifications of the embodiments of the invention can be substituted without departing from the principles of the invention, as will be evident to those skilled in the art.
As previously discussed the present invention provides a glassy matrix preferably formed by crosslinking a mixture of a functionally-terminated silicone and an alkoxy functionalized siloxane to provide an interpenetrating polymer network (xe2x80x9cIPNxe2x80x9d) of glass and silicone. Grafted to the matrix is a material capable of microphase separation. The material capable of microphase separation is at least two liquid materials, at least one of which is graftable to the matrix. Also included in the material is a freezing point depression agent such as a polyol or salt hydrate. Such a freezing point depression agent may itself be a material capable of microphase separation. Such a glassy matrix is described in U.S. Ser. No. 09/586,378 filed Jun. 2, 2000, the disclosure of which is incorporated by reference herein in its entirety.
Alternatively, the anti-icing composition comprises a crosslinked mixture of an an epoxy, an alkoxy-functionalized siloxane and a silane capable of compatabilizing the epoxy and the alkoxy-functionalized siloxane to provide an epoxy-modified interpenetrating polymer network of glass and epoxy. Grafted to the matrix is the material capable of microphase separation. The composition also includes a freezing point depression agent.
The glassy matrix is crosslinked using a titanium or tin catalyst. Suitable catalysts include titanium, without limitation, alkoxides such as titanium methoxide, titanium ethoxide, titanium isopropoxide, titanium propoxide, titanium butoxide, titanium diisopropoxide (bis 2,4-pentanedionate), titanium diisopropoxide bis(ethylacetoacetao) titanium ethylhexoxide, and organic tin compounds such as dibutyl tin diacetate, dibutyltin laurate, dimethyl tin dineodecanoate, dioctyl dilauryl tin, and dibutyl butoxy chlorotin, as well as mixtures thereof.
The matrix formulation can include a silica gel including propionic or octonoic acid to inhibit the crosslinking reaction so that the anti-icing composition can be applied to the surface to be coated. The glassy matrix can be formed by using a Sol-Gel process such as described in U.S. Ser. No. 09/586,378. Other methods of forming the matrix will be within the skill of one in the art. The matrix formulation may also include fillers such as, without limitation, fumed silica, mica, kaolin, bentonite, talc, zinc oxide, iron oxide, cellulose, pigments, polytetrafluoroethylene powder, ultra high molecular weight polyethylene powder, high, medium and low molecular weight polyethylene powder, or other fillers, as will be readily apparent to those skilled in the art. The glassy matrix formulation may further include carbon black, silicon powder, doped zinc oxide and polyaniline. Such additives can be used to modify the resistive or dielectric or both properties of the anti-icing composition.
The glassy matrix serves to provide a carrier or support material for the material capable of microphase separation. The matrix provides good adhesion to the surface being coated, as well as, toughness, crack resistance, durability, abrasion resistance and stability in the particular environment.
The anti-icing composition of the present invention also includes a material capable of microphase separation. The material comprises at least two liquids, which in addition to its separation aspects, one of which is capable of being grafted into the glassy matrix. A material capable of microphase separation is a material that because of physical or chemical interactions between (among) the liquid materials substantially continuously phase separates or moves.
Suitable functionally-terminated silicones include silanol terminated, vinyl terminated and amino terminated polydimethylsiloxane. Such silicones have low tear strength and can be toughened by incorporating glass (SiO2) into the structure. Thus, an alkoxy-functionalized siloxane can be included. Suitable alkoxy-functionalized siloxanes include polydiethoxysiloxane, tetraethoxy silane, tetramethoxy silane, and polydimethoxy siloxane.
One manner of forming the glassy matrix is using a Sol-Gel process employing a catalyst agent such as an organotitanate compound, for example, a titanium alkoxide compound such as, but not limited to, titanium methoxide, titanium ethoxide, titanium isopropoxide, titanium propoxide, titanium butoxide, titanium ethylhexoxide, titanium diisopropoxide (bis 2,4 pentanedionate), titanium diisopropoxide bis(ethylacetoacetate), or any other type of titanium alkoxide compound. These titanium alkoxide compounds can be used separately or in any combination. Although titanium alkoxides are given as examples, other organotitanate compounds can be used. The glassy matrix can also include a carboxylic acid compound. Silica gel is optional to inhibit the crosslinking reaction. Silica gel is used if storage over a long period of time is an issue. This is because it is believed to store moisture. Alternatively, only silica gel can be used in place of the carboxylic acid compound. However, this does not work as well and a lot of silica gel is required.
With respect to the Sol-Gel process, as is well know to those of ordinary skill in the art, the Sol-Gel process is conventional, and typically produces a Sol-Gel glass which results from an optically transparent amorphous silica or silicate material produced by forming interconnections in a network of colloidal submicrometer particles under increasing viscosity until the network becomes completely rigid, with about one-half the density of glass.
One of the materials capable of microphase separation and graftable into the glassy matrix may be a vinyl terminated polydimethyl siloxane polymer reacted with dimethylethoxy silane or 1,1,3,3 tetramethyl disiloxane and triethyl silane using a hydrosilylation reaction. Another microphase separated material which can be employed is a methylhydrosiloxane polymer which is side-chain grafted with octene and vinyltriethoxy silane using a platinum-activated hydrosilylation reaction.
Alternatively, the glassy matrix can comprise a crosslinked mixture of an epoxy, an alkoxy-functionalized siloxane and a silane capable of compatabilizing the epoxy and the alkoxy-functionalized siloxane to provide the interpenetrating polymer network of glass and epoxy. Epoxy compounds are well know and are described in, for example, U.S. Pat. Nos. 2,467,171; 2,615,007; 2,716,123; 3,030,336; and 3,053,855 which are incorporated herein in their entirety by reference. Useful epoxy compounds include the polyglycidyl ethers of polyhydric polyols, such as ethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,5-pentanediol, 1,2,6-hexanetriol, glycerol and 2,2-bis(4-hydroxy cyclohexyl) propane; the polyglycidyl esters of aliphatic or aromatic polycarboxylic acids, such as oxalic acid, succinic acid, glutaric acid, terephthalic acid, 2,6-naphthalene dicarboxylic acid and dimerized linoleic acid; the polyglycidyl ethers of polyphenols, such as 2,2-bis(4-hydroxyphenyl) propane (commonly known as bis-phenol A), 1,1-bis(4-hydroxyphenyl) ethane, 1,1-bis(4-hydroxyphenyl) isobutane, 4,4xe2x80x2-dihydroxybenzophenone, 2,2-bis(4-hydroxyphenyl) butane, bis(2-dihydroxynaphthyl) methane, phloroglucinol, bis(4-hydroxyphenyl)sulfone, 1,5-dihydroxynaphthalene, and novolak resins; with the polyglycidyl ethers of a polyphenol, polybisphenol A-epichlorohydrin glycidyl end-capped and polybisphenol F-epichlorodydrin glycidyl end-capped. being currently preferred.
Generally the preferred epoxy compounds are resins having an epoxide equivalent weight of about 100 to 2000, preferably about 110 to 500. A presently preferred epoxy is EPON 862 available from Resolution Performance Products, Houston, Tex.
Suitable additives for the epoxy modified matrix include curing agents (e.g., Ancamide 862, a polyamide curing agent available from Air Product, Allentown, Pa). Silanes capable of compatibilizing the epoxy and the alkoxy-functionalized siloxane include 3-(glycidoxypropyl)trimethoxysilane) and amino propyl triethoxy silane. Benzyl Alcohol can also be used to help compatibalize the epoxy and alkoxy-functionalized siloxane.
The freezing point depression agent is preferably a polyol which reduces the freezing point of water that comes in contact with the surface to which the anti-icing composition is applied. The freezing point depression material can itself be liquid phase separable and will move or bloom to the exposed surface. Suitable freezing point depression agents include various alcohols, polyols, water soluble salts and polyol fatty acid esters. Preferred agents include polypropylene glycol, polyethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, ethylene glycol, sorbitol, glycerol, sodium acetate and potassium acetate. Such agents can be combined with other freezing point depression agents, for example, choline and various salts such as magnesium chloride hexahydrate, CaCl2, and NaCl.
Either of the anti-icing compositions preferably comprise about 20 to 90 percent by weight of the glassy matrix; the liquid material capable of liquid phase separation preferably comprises about 1 to 30 percent by weight of the composition; and the freezing point depression agent preferably comprises about 0.1 to 50 percent by weight of the composition. As previously stated the various compositions may also include additives which modify the resistive or dielectric properties of the coating. Such additives and modifications are important when used in aircraft wherein radar absorbent materials are to be used, e.g., the U.S. military""s B2 bomber, to protect aircraft from lightening strikes, and to reduce electrostatic discharge.
In operation, the anti-icing composition of the present invention can be applied by roll-coating, brush, spray coating dipping and the like. As discussed above, it is preferred that the user, mix the catalyst with the other components right before or substantially contemporaneously with application. The composition is preferably applied at a thickness of about 0.25 mm to 1.0 mm.